Introduction of walking beam heat treatment furnac

2022-08-17
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Introduction to the walking beam heat treatment furnace with excellent performance

1. Overview

the walking beam heat treatment furnace project of North heavy industry group, undertaken by Beijing Fujing technology company, was put into normal production and operation in March this year. The stepping furnace is used for normalizing heat treatment of train shaft blanks after forging and forming. After being put into operation, the furnace was comprehensively tested. The test results show that the technical and economic indicators of the stepping furnace are better than or in line with the relevant national standards, and the heat treated products are qualified after being tested by the relevant national departments

the main technical properties of the walking beam heat treatment furnace are as follows:

(1) the effective length of the furnace: 15080mm, which is divided into preheating section, heating section and soaking section along the length direction

(2) effective width of furnace: 2784mm

(3) furnace clearance height: 1100mm

(4) furnace service temperature: 860 ℃ (normalizing), 550 ℃ (tempering)

(5) air preheating temperature: 400 ℃

(6) furnace temperature uniformity: measured value of heating section and soaking section ± 5 ℃

(7) furnace production capacity: 5.1t/h

(8) workpiece size: ① 220 x 2500mm

(9) stepping machine form: slope roller type

(10) step cycle: 2min

(11) fuel and consumption: generator gas 1500nm3/h

(12) installed power of furnace: 48kW

2. Pulse combustion heating technology

the combustion condition of the burner is the main factor affecting the temperature uniformity of the furnace. The stepping heat treatment furnace adopts the combustion pulse controller, pneumatic executive control valve, flame monitoring and automatic ignition system produced by Krom company of Germany, which solves the problem that the high content of impurities such as tar and ash in the producer gas affects the sensitivity of the actuator. The automatic control can be realized smoothly

the adjustment ratio of traditional burner is generally about 1:4-5. When the burner works at rated load, the gas flow rate, flame shape and thermal efficiency can reach the best state. However, when the furnace temperature reaches the process setting temperature for insulation, the burner load is reduced to less than half of the rated load, the heating load is reduced, the gas flow rate is greatly reduced, the flame shape cannot meet the requirements, and the thermal efficiency is sharply reduced. Although the adjustment ratio of the high-speed temperature regulating burner reaches about 1:10, when it works under 50% of the rated load, the above indicators will also have a large gap from the design requirements. Pulse combustion is not the case. In any case, there are only two working states of the burner, one is the best load work, and the other is not work. Just adjust the temperature by adjusting the time ratio of the two states, so that the use of pulse combustion can make up for the defect of low burner adjustment ratio, and it can still ensure that the burner works in the best combustion state when heat preservation or low temperature control is required. When using the high-speed burner, the gas ejects quickly, forming a negative pressure around, sucking a large amount of flue gas in the furnace into the main combustion area for full mixing, prolonging the stagnation time of flue gas in the furnace, increasing the contact time between flue gas and heated workpiece, thus improving the heat transfer efficiency. In addition, the flue gas in the furnace is fully mixed with the gas, making the gas temperature close to the flue gas temperature in the furnace, and improving the uniformity of the temperature field in the furnace, Reduce the direct thermal impact of high-temperature gas on the heated workpiece

the regulation of combustion atmosphere is an essential link to improve the performance of industrial kilns. The traditional continuous combustion control can only accurately control the combustion atmosphere in the furnace by measuring the residual oxygen in the flue gas, feeding it back to the combustion atmosphere controller, and then adjusting and controlling the output of the combustion air flow actuator in real time. Due to the reliability, service life and price of zirconia sensor for detecting residual oxygen in flue gas, its actual use in industrial sites is limited. Some kiln automatic control systems simply use a proportional regulator to make the flow of combustion supporting air in a fixed proportion to the flow of fuel, but this method has to leave a large margin coefficient of combustion supporting air, which cannot meet the best energy conservation and control requirements. Using pulse combustion control mode, the fuel pressure and combustion air pressure can be adjusted to appropriate values at one time. After the system is put into operation, it is only necessary to keep these two pressures stable. It is much simpler to measure and control the pressure than the flow. Full automatic control or manual control can be adopted according to the actual situation of the system

3. Automatic control system

the control system of the heat treatment furnace adopts the upper control system composed of Advantech industrial computer and Siemens PLC controller, and adopts the advanced on-site sampling and inspection of unqualified food to burn all the system structure of the line, which fully automatically controls the workpiece feeding and unloading process, fuel combustion process, furnace thermal system and physical parameters, and comprehensively manages the production process. German Krom products are selected for pulse combustion and monitoring of high-speed burners. The control software first uses the wincc5.0 system that can be developed with Windows2000 as the operating platform. The above control system ensures the continuous operation of the furnace, stable performance, high accuracy level and convenient operation and maintenance. The software control system, hardware equipment level and technical performance of the heat treatment furnace are in a leading position in the same industry in China. The system has the following functions:

(1) real time monitoring the temperature, furnace pressure, gas pressure, combustion air pressure, cooling water pressure, fuel flow and other parameters in the furnace since the founding of new China

(2) it has the alarm and protection functions of the upper and lower limits of the physical quantity setting parameters, and the alarm printing function. The upper and lower limits of the alarm are set by the user, and the alarm records can be stored. The user can query and print at will

(3) the temperature rise and fall of each section in the furnace can be controlled according to the temperature value or temperature curve set by the process

(4) automatically adjust and control the furnace pressure

(5) control the feeding and discharging speed of the heat treatment furnace

(6) it has the function of historical data query, which can store, display and print historical data according to users' needs

(7) it has the function of report printing, and can print the shift report, monthly report offline in real time

(8) it has a dynamic process diagram, which can display the process flow diagram of the whole furnace, real-time and dynamic display the parameters of each point, and real-time and dynamic display the flame combustion state in the furnace

4, energy-saving lining structure

in order to shorten the construction cycle and obtain good heat preservation and energy saving effect, the top of the furnace adopts high alumina phosphate prefabricated parts with good performance, the furnace wall and bottom are built with clay plastic as a whole, and composite masonry is formed with heat insulation bricks, calcium silicate board, etc., so as to improve the integrity, tightness and heat insulation of the furnace, so as to obtain the minimum heat dissipation loss and the maximum service life of the furnace lining. The measured temperature of the outer surface of the furnace wall is lower than 50 ℃, and the masonry form of each part of the furnace is as follows:

furnace top: 300mm high aluminum phosphate prefabricated parts

furnace wall: clay brick 232mm: light clay brick 116mm; Asbestos free calcium silicate board 80mm, with a total thickness of 428mm

furnace bottom: clay brick and clay plastic 116+136mm; Light clay brick 136mm; Asbestos free calcium silicate board 80mm; Asbestos board 20mm, total thickness 488mm

5. Structural characteristics and orbital motion device of walking beam furnace the bottom of walking beam furnace includes movable bottom and fixed bottom. In this scheme, there is one active bottom and two fixed bottom. The fixed bottom is fixed on the H-shaped steel beam at the bottom of the furnace, and the movable bottom is fixed on the walking mechanical translation mechanism at the bottom of the furnace through the steel structure. The bottom of the furnace is inlaid with serrated joists made of heat-resistant steel, which can be used in the medium and long term at a furnace temperature of 1000 ℃. The axles are arranged in a single row on the furnace bottom, and 50 axles can be placed on the joist in the furnace. The joist is cast into a V-shaped tooth groove with arc, and the tooth pitch (axle center distance) is 300mm. The step pitch of the movable bottom joist is 260mm, which is smaller than the tooth pitch of the fixed bottom joist

therefore, the axle itself will rotate an angle with the tooth shape each time, so as to ensure that the axle heating is more uniform and prevent the axle from bending and deformation in the furnace

the stepping machine adopts the slope roller type, which is composed of a set of translation frame, a set of lifting frame, 12 rollers, a set of translation centering device, a set of lifting centering device, a translation hydraulic cylinder, a lifting hydraulic cylinder, 12 sets of lifting inclined rail seats and other equipment

The translation mechanism is used to support the water seal groove, the movable bottom and the axle placed on the movable bottom. Its structure adopts section steel welding structure

the translational centering device is symmetrically arranged along the center line of the furnace to focus on the center of the translational mechanism, a total of 4 sets, which are used for the centering operation of the translational mechanism to ensure that its movement direction is always parallel to the center line of the furnace, so as to reduce the deviation of the trolley shaft in the furnace, so that the axle can be accurately transported from the feeding end to the discharging end

the lifting centering device is symmetrically arranged at the center of the lifting mechanism along the center line of the furnace, with a total of 4 sets. Its function is the same as that of the translational centering device. The accurate operation of the axle in the furnace is the result of the joint action of the two

one horizontal moving hydraulic cylinder with displacement sensor is used to drive the translation mechanism for horizontal movement. The translation cylinder is set on the central line of the furnace at the charging end, and the piston rod end is hinged with the translation frame. When the piston rod of the hydraulic cylinder expands and contracts, the driving translation mechanism advances or retreats in the horizontal direction

one lifting and moving hydraulic cylinder with displacement sensor is used to drive the translation mechanism to move up and down. The lifting cylinder is located on the center line of the furnace at the charging end. The piston rod end is hinged with the translation mechanism. When the piston rod of the hydraulic cylinder expands and contracts, the driving translation mechanism rises or falls along the inclined rail surface

the furnace area is equipped with an independent hydraulic system to provide power source for the stepping mechanical movement of the heat treatment furnace, and meet the requirements of various circular movements of the stepping bottom for step distance, speed and impact load, so that it can complete various set circular movements within the predetermined movement cycle

in terms of system control, the system is composed of speed regulation control circuit, direction control circuit, buffer balance control circuit, safety overflow and pressure control circuit, as well as the value forbidden by the auxiliary needle. It is important to check whether there is a resonance auxiliary system control circuit around the experimental machine. Each circuit has independent control function and can work together to make the whole hydraulic system achieve the best control state

the proportional electromagnetic directional valve and pressure compensator are used to realize stepless control of the working flow of the whole sample system, which is an open innovation and overseas innovation of multinational enterprises, and fully meet the requirements of the working oil cylinder for the system output flow, so as to finally make the step bottom reach the movement speed required by the process. The buffer balance control circuit is composed of balance valve, overflow valve, one-way valve, etc. Its function is to minimize the impact inertia caused by the change of speed at the beginning and end of the lifting and translation movement of the walking beam, and realize the balance transition of the moving speed

the safety overflow and pressure control circuit is composed of electromagnetic overflow valve, pressure control switch and other components. Its function is to realize the loading and unloading of the whole system and stabilize the working pressure of the system, and it can overflow or control the motor to cut off power under the condition of overvoltage, so as to ensure that the whole system will not be damaged due to accidents

auxiliary systems include oil filtration system, oil temperature automatic control system, liquid level control and alarm, oil filter blockage alarm safety interlock, pressure remote transmission display, etc

because the computer is used to participate in the whole control process of the hydraulic system, and the proportional directional valve and constant pressure variable pump are used, the system has the following main characteristics: fast response speed, high control accuracy, large control flexibility, high degree of automation, stable system performance, etc

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